With my new one-a-day query submission system, the form letter rejection emails are starting to trickle in at a faster rate. This buoys me. Each rejection email is one email closer to my ultimate YES email. (If, indeed, I'm fated to get one.)
And so my advice to my fellow aspiring agented writers is to embrace rejection! It's part of the process for 99.9+ % of us. Yes, form rejection letters leave no clue as to how to change or improve your story and and query, but maybe they they don't need improving. Maybe they just haven't landed in the right emailbox yet! Of course, my other pieces of advice would be to always leave yourself open to improvement, choose your agents carefully, and craft your queries FOR your chosen agents as much as you reasonably can.
Don't let fear of yet another rejection hold you back. What if you decide to stop querying just when the very next agent you would've queried would've been THE ONE? Better to check that, and query the agent next on your list!